Disposable retortable containers are typically formed from either metallic foils, such as aluminum foil, or plastics resins. These containers include a lip portion outwardly extending in a generally horizontal direction along the top opening thereof, providing a sealing region for a closure element.
Membrane closure elements for such retortable containers are also known. Typically, these membranes are heat and/or adhesively bonded to the lip of the container. The seal between the membrane and the container must be capable of withstanding the retort sterilization process, which process occurs in the presence of steam and/or water at temperatures of 250.degree. F. (121.degree. C.) and higher. In order to accomplish this, the membranes in the past have required seal strengths such that peeling of the membrane from the container by hand was impossible.
Attempts have been made to provide a peelable membrane structure. Thus, U.S. Pat. Nos. 3,946,871 and 3,946,872 describe membranes in which the seal between an aluminous metal layer and a plastics resin layer is peeled by breaking of the plastics resin layer. Although it is stated in these patents that such a membrane is retortable, it has been found that the failure rates for these containers during retorting is unacceptably high. My U.S. Application Ser. No. 279,952, filed July 1, 1981, now U.S. Pat. No. 4,381,848 solved the problem of retort failure by providing an aluminum foil layer as the peeled layer.
In each of these structures, peeling of the membrane results in an opened container, with the food or other product exposed. Recently, the increased popularity of microwave ovens and vending machine operations have produced the need for a peelable membrane for retortable containers in which the barrier layer of the membrane, which layer provides a portion of the ability to withstand retorting and which layer is typically a barrier material to microwaves, such as aluminum foil, is removed and a protective covering remains on the container after peeling, to provide protection and/or splatter resistance for the contents of the container during reheating or cooking in a microwave or other oven.
It is thus a primary object of the present invention to produce a peelable membrane structure for containers which can consistently successfully withstand the retort sterilization process and which provides a protective covering after peeling which can be opened after reheating or cooking in a microwave or other oven.